RFC: Rename PPC_MPC6XX to PPC_OEA

[Matt Thomas <matt%3am-software.com@localhost>]

Very soon, I'd to rename to PPC_MPC6XX to PPC_OEA(*) (and anything
mpc6xx* to oea*).  While this may seem pendantic to some, there's
a real reason to do this.

The IBM Power3/Power4 are OEA implementations, but OEA 64bit
implementations.  With a few macros, much of the 6xx assembly
can be reused for the OEA64 processors.

While we could keep the PPC_MPC6XX name, it seems wrong to use
it for the IBM OEA 64bit processors as well.

(*) OEA is acronym for "Operating Environment Architecture" which is
the privileged environment defined in PowerPC "green book".

--
Matt Thomas               Internet:   matt%3am-software.com@localhost
3am Software Foundry      WWW URL:    http://www.3am-software.com/bio/matt/
Cupertino, CA             Disclaimer: I avow all knowledge of this message